The present invention relates to ink input systems for use in high speed, high volume printing processes using viscous ink such as in offset lithographic printing.
In the field of high speed lithographic printing, ink is continuously conveyed from an ink source by means of a series of rollers to a planographic printing plate on a plate cylinder in a lithographic printing press. Image portions of the printing plate accept ink from one or more of the last of a series of inking rollers and transfer a portion of that ink to a blanket cylinder as a reverse image from which a portion of the ink is transferred to form a correct-reading image on paper or other materials. It is also essential in conventional lithographic printing processes that a dampening solution containing water and proprietary additives be conveyed continuously to the printing plate whereby transferring in part to the non-image areas of the printing plate the water functions to keep those non-image areas free of ink.
In conventional printing press systems, the ink is continuously made available in varying amounts determined by cross-press column input control adjustments to all parts of the printing plate, including both image and non-image areas. In the absence of the dampening solution, the printing plate will accept ink in both the image and non-image areas of its surface.
Lithographic printing plate surfaces in the absence of imaging materials have minute interstices and a hydrophilic or water-loving property to enhance retention of water, that is the dampening solution, rather than ink on the surface of the plate. Imaging the plate creates oleophilic or ink-loving areas according to the image that is to be printed. Consequently, when both ink and dampening solution are presented to an imaged plate in appropriate amounts, only the ink tending to reside in non-image areas becomes disbonded from the plate. In general, this action accounts for the continuous ink and dampening solution differentiation on the printing plate surface, which is essential and integral to the lithographic printing process.
Controlling the correct amount of dampening solution supplied during lithographic printing has been an industry-wide problem ever since the advent of lithography. It requires continual operator attention since each column adjustment of ink input may require a change in dampener input. Balancing the ink input that varies for each column across the width of the press with a uniform dampening solution input across the width of the press is at best a compromise. Consequently, depending upon which portion of the image the operator has adopted as his standard of print quality at any given time during the printing run, the operator may need to adjust the ink input from ink injectors at correspondingly-located cross-press positions. As a result, the dampening solution to ink ratio at that position may become changed from a desired value. Conversely, the operator may adjust a dampener input for best ink and dampening solution balance at one inking column, which may adversely affect the ink and dampening solution balance at one or more other cross-press locations. Adjustments such as these tend to occur repeatedly throughout the whole press run, resulting in slight to significant differences in the quality of the printed image throughout the run. In carrying out these adjustment operations, the resulting images may or may not be commercially acceptable, leading to waste in manpower, materials, and printing machine time.
Certain commercially successful newspaper printing configurations rely on the inking train rollers to carry dampening solution to the printing plate. Notable among these are the Goss Metro, Goss Metroliner, and the Goss Headliner Offset printing presses which are manufactured by the Graphic Systems Division of Rockwell International Corporation. In these alternative configurations, the dampening solution is combined with the ink on an inking oscillator drum such that both ink and water are subsequently and continuously transferred to the inking form rollers for deposition onto the printing plate. These conventional lithographic systems require complex adjusting systems and mechanisms for the ink injectors in order to maintain ink and dampening solution balance, such as disclosed in U.S. Pat. No. 3,534,663.
The present invention overcomes the aforementioned problems, difficulties and inconveniences, yet retains all of the principles essential to prior art variable-input inking systems. Accordingly, in this improvement the mechanical adjustments of the ink injectors are eliminated resulting in a more dependable, smaller and simplified printing fluid input apparatus.